1. Field of the Invention
The present invention relates generally to the field of motorcycle engines. More specifically, the present invention discloses an improved breather for crankcase gases from a motorcycle engine.
2. Statement of the Problem
The reciprocating motion of the pistons in the cylinders of a motorcycle engine causes pressure swings in the crankcase that must be vented for efficient operation of the engine. One response to this problem was to simply vent the gases and entrained oil droplets from the crankcase. For example, this can be done through a length of flexible tubing that extends downward toward the pavement. This creates a mess, particularly if the motorcycle is parked in a garage or on a driveway. Nonetheless, this was the solution used in many Harley-Davidson motorcycle engines until the mid-1980s.
Current environmental regulations require that motorcycle manufacturers must route gases vented from the crankcase through the engine intake to reduce pollution. Many modern Harley-Davidson engines, such as the “Evolution” and “Twin Cam” engines, route gases from the crankcase upward through the push rod covers 14 into the rocker boxes 12 above the cylinder heads as shown in FIGS. 2(a)-2(c). An umbrella valve 15 allows gas flow in only one direction through each rocker box. Some oil droplets are trapped at this point in the rocker box 12 and drain back through the engine via a drain hole 17 adjacent to the umbrella valve 15. The remaining crankcase gases and entrained oil droplets exit through a threaded fitting 16 and tube leading to the air intake for the carburetor (not shown). Unfortunately, this tends to “gunk up” the carburetor and intake manifold, and reduces engine performance.
As a result, a number of after-market companies have developed retrofit breathers to directly vent crankcase gases, instead of routing these gases through the engine. These breathers typically vent the crankcase gases through a small metal chamber or canister with slots or openings in its side or bottom. This also creates a mess by spraying oil droplets against the exterior of the engine or the rider's leg. Therefore, a need exists for a breather that can be readily retrofit to a motorcycle engine and that effectively traps oil droplets entrained with the crankcase gases.
The prior art in this general field includes the following:
InventorU.S. Pat. No.Issue DateUssery3,834,365Sep. 10, 1974DeBruler4,453,525Jun. 12, 1984Sakano et al.4,459,966Jul. 17, 1984Blanc et al.5,205,848Apr. 27, 1993Sanders5,551,409Sep. 3, 1996Daidone6,105,560Aug. 22, 2000Wilson6,167,849Jan. 2, 2001Knowles6,729,316May 4, 2004Michel6,925,994Aug. 9, 2005
Wilson discloses a crankcase breather for motorcycles that has a canister with a removable lid and a downwardly-extending inlet tube. The filter element is attached to the outlet port above the lid, rather than being placed inside the canister. Any oil collecting in the canister can be drained through a petcock in the bottom of the canister.
DeBruler discloses a canister and a flow path similar to the Wilson patent. A thin filter element extending across the midsection of the canister traps sludge and liquids in the bottom of the canister. The outlet port routes vapors to the intake manifold of the engine, rather than directly into the atmosphere.
Ussery shows another example of a crankcase breather that uses a canister with an outlet in the lid, Ussery uses a small quantity of fuel in the canister as the filter media.
Michel, Daidone, Sanders and Blanc et al. show other examples of breather tubes and vents with filters or baffles. Knowles and Sakano et al. show other examples of systems that filter crankcase gases and recycle them through the engine.
3. Solution to the Problem
None of the prior art references discussed above show a breather having the structure of the present invention. In particular, the present invention creates a flow path within the breather that traps the entrained oil droplets in the bottom of the container and filter media. The container can be periodically unthreaded from the stem to remove the accumulated oil.